1. Field of the Invention
Example embodiments relate generally to nuclear reactors, and more particularly to a method and apparatus for an alternative remote spent fuel pool cooling system for a Light Water Reactor (LWR) nuclear reactor. The cooling system may be particularly beneficial in the event a plant emergency that causes plant electrical power to be disrupted, or normal cooling of the spent fuel pools to otherwise become impaired. The cooling system may also be used to supplement fuel pool cooling via the conventional fuel pool cooling and cleanup system.
2. Related Art
FIG. 1 is a cut-away view of a conventional boiling water nuclear reactor (BWR) reactor building 5, which is one example of a light water reactor (LWR). It should be understood that this is merely an example, as other reactor design layouts may be used for other LWRs. The spent fuel pools 10 are storage pools used to store spent fuel 12 that remain following the use of the fuel to power the BWR reactor 1. The spent fuel pools 10 are generally positioned in locations adjacent to, and toward the top of, the reactor 1 (as shown in FIG. 1, the spent fuel pool 10 is located in secondary containment, outside of the steel containment vessel 3 and concrete shell 4 protecting reactor 1). The spent fuel pool may be located at a plant elevation that is above a location of the suppression pool 2. It should be noted that in other reactor designs, the spent fuel pool may be located at a same plant elevation as the reactor, or at an elevation that is below the reactor. The spent fuel 12 is generally stored in the spent fuel pools 10 for a period of at least 5 years before being sent to reprocessing or cask storage. The spent fuel pools 10 are typically 40 feet or greater in depth, with the bottom 14 feet being equipped with storage racks that hold the fuel assemblies that are removed from the reactor. About 8 feet of water (above the top of the spent fuel, itself) is generally needed to keep radiation levels in the spent fuel pools 10 within acceptable limits (see spent fuel pool water level 10b, which is above the spent fuel 12).
A flow of cooling water, provided by conventional fuel pool cooling and cleanup system (not shown), provides shielding from radiation and maintains the spent fuel pools 10 at cool temperatures that ensure the cooling water does not boil (thereby exposing the spent fuel to open air). The conventional spent fuel cooling pumps provide cooling of the spent fuel pools. Specifically, the conventional fuel pool cooling pumps transfer the water from the spent fuel pool to the fuel pool cooling and cleanup system. The conventional fuel pool cooling and cleanup system cools and cleans the water, using a heat exchanger and demineralizers (removing some radioisotopes, and other impurities). The fuel pool cooling pumps then send the cool, clean water back to the spent fuel pool 10.
During a serious plant accident, normal plant electrical power may be disrupted. In particular, the plant may be without normal electrical power to run the conventional fuel pool cooling pumps, or operate the fuel pool cooling and cleanup system. If electrical power is disrupted for a lengthy period of time, disruption in the use of the fuel pool cooling and cleanup system may cause water in the spent fuel pool to warm and eventually boil. When enough boiling occurs, water levels in the pool may drop to levels that no longer provide enough cooling water to effectively shield radiation that may be caused by the spent fuel. In very serious emergencies, water in the spent fuel pool may boil and evaporate to the point that the spent fuel may become exposed to open air. Such an emergency may pose grave dangers for plant personnel and the environment.
In a plant emergency, even if the spent fuel in the spent fuel pool is not exposed to open air (in the event of a worst-case accident scenario), there are still concerns with radiation leakage leaving the spent fuel pool and escaping to the environment. In particular, the fuel pool cooling and cleanup system may become over-loaded in handling the cooling and radiation reduction needs of the spent fuel pool. This may particularly be the case, in the event that fuel damage occurs in the spent fuel pool. If the integrity of the fuel rods within the spent fuel pool becomes jeopardized, use of the fuel pool cooling and cleanup system may pose risks to plant personnel and the environment, as highly radioactive water (above acceptable design limits) may be transferred to the fuel pool cooling and cleanup system. In such a scenario, the fuel pool cooling and cleanup system may be unable to assist in effectively reducing radiation levels of the spent fuel pool water. Therefore, the transfer of the highly radioactive water to the fuel pool cooling and cleanup system may, in and of itself, cause a potential escalation in the abilities to contain harmful radioactive isotopes within secondary containment.